Organic compound and organic light emitting device using the same

ABSTRACT

Disclosed is a compound represented by formula 1:
     [formula 1]   

                         
wherein each of A, X, Y, Y′ and Y″ has the same meaning as described herein. When used in an organic light emitting device, the compound represented by formula 1 has at least one function selected from the group consisting of hole injection, hole transport, light emitting, electron transport, electron injection, etc., depending on the type of each unit forming the trimer or substituents in each unit. An organic light emitting device is also disclosed. The organic light emitting device includes a first electrode, an organic film having one or more layers and a second electrode, laminated successively, wherein at least one layer of the organic film includes at least one compound represented by formula 1.

TECHNICAL FIELD

The present invention relates to a new organic compound and an organiclight emitting device using the same.

BACKGROUND ART

In general, the so-called “organic light emitting” phenomenon (organicelectroluminescence) refers to a phenomenon in which electric energy istransformed into light energy by means of an organic substance.Particularly, when an organic film is disposed between an anode and acathode and then electric potential is applied between both electrodes,holes and electrons are injected into the organic film from the anodeand the cathode, respectively. When the holes and electrons injected asdescribed above are recombined, excitons are formed. Further, when theexitons drop to a ground state, lights are emitted.

In addition to the above-described organic light emitting mechanism inwhich light emission is made by recombining of charges injected fromboth electrodes, there is another mechanism in which holes and electronsare not injected from external electrodes but are generated by anamphoteric charge-generating layer under the application of alternatingcurrent voltage, as in the case of a conventional inorganic thin filmlight emitting device, and the holes and electrons move to an organicthin film layer, resulting in light emission (Appl. Phys. Lett., 85(12),2382-2384).

Since POPE, KALLMAN, et al. found electro-luminescence in anthracenesingle crystal in 1963, active research and development into OLEDs(Organic Light Emitting Devices) have been made up to now. Recently,organic light emitting devices have been used in flat panel displaydevices, lighting devices, etc. Such organic light emitting devices havebeen developed so rapidly that performance as display devices isremarkably improved and various applied products are developed.

In order to manufacture more efficient organic light emitting devices,many attempts have been made to manufacture an organic film in thedevice in the form of a multilayer structure instead of a monolayerstructure. Most of currently used organic light emitting devices have astructure in which an organic film and electrodes are deposited. Theorganic film generally has a multilayer structure including a holeinjection layer, hole transport layer, light emitting layer, electrontransport layer and an electron injection layer.

It is known that OLEDs are characterized by high brightness, highefficiency, low drive voltage, color changeability, low cost, etc.However, in order to have such characteristics, each layer forming anorganic film in a device (for example, a hole injection layer, holetransport layer, light emitting layer, electron transport layer andelectron injection layer) must be formed of more stable and efficientmaterials.

A method of doping a light emitting host with a fluorescent compound soas to increase the light emitting efficiency of a multilayer-structuredOLED was disclosed. Particularly, according to Tang, et al. (J. Appl.Phys. Vol. 65 (1989), p. 3610), light emitting efficiency can beimproved by mixing a fluorescent compound having a high quantumefficiency (for example, coumarin pigments or pyran derivatives) in asmall amount with a light emitting host. In this case, light having adesired wavelength can be obtained depending on the type of thefluorescent compound. However, when Alq3 is used as electron transportmaterial and drive voltage is increased to obtain high brightness, greenlight emission based on Alq3 may be observed in addition to lightemission based on the doped fluorescent compound. This is problematic interms of color purity, particularly when the color of light to beemitted is blue. It is known that such a problem results from a narrowband gap between the HOMO (highest occupied molecular orbital) and theLUMO (lowest unoccupied molecular orbital) of Alq3. Such a narrow bandgap results in exciton diffusion from a light emitting layer to Alq3,thereby causing light emission based on Alq3.

The use of hole block material has been reported as another method forincreasing light emitting efficiency of OLEDs, wherein the hole blockmaterial includes3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ),bathocuproine (BCP), etc. (Jpn. J. App. Phys. Part 2, 1993, 32, L917).However, the above-mentioned materials show poor durability and have aserious problem of deterioration of a device, particularly when thedevice is subjected to continuous light emission while being stored athigh temperature. Moreover, there are additional problems in that theabove-mentioned materials should be provided as a layer separated from alight emitting layer, and that drive voltage increases due to a largeband gap between the HOMO and the LUMO when the materials are used.

Therefore, in order to overcome the problems occurring in the prior artand to further improve characteristics of OLEDs, it is necessary todevelop more stable and efficient materials that may be used in OLEDs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 5 are schematic views each illustrating the structure of anorganic light emitting device (OLED) that may be applied to the presentinvention, wherein reference numeral 101 is a substrate, 102 is ananode, 103 is a hole injection layer, 104 is a hole transport layer, 105is a light emitting layer, 108 is a hole block layer, 106 is an electrontransport layer and 107 is a cathode 107.

FIG. 6 is a graph showing the current-voltage relationship of the OLEDaccording to Example 1 and that of the OLED according to ComparativeExample 1.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to improve durability and/orefficiency of an organic light emitting device by an organic substancecapable of carrying out at least one function selected from the groupconsisting of hole injection, hole transport, hole block, lightemitting, electron transport, electron injection, and buffering betweenan anode and a hole injection layer, wherein the organic substance isdesigned by using a cyclic trimer core structure represented by thefollowing formula 1.

According to an aspect of the present invention, there is provided acompound represented by formula 1:

wherein

A is B or N;

X is N or CR₀, wherein R₀ is selected from the group consisting of ahydrogen atom (H), halogen atom, nitrile group (CN), nitro group (NO₂),formyl group, acetyl group, benzoyl group, amide group, styryl group,acetylene group, quinoline group, quinazoline group, phenanthrolinegroup, cuproine group, anthraquinone group, benzoquinone group, quinonegroup, acridine group, substituted or non-substituted alkyl group,substituted or non-substituted aryl group, substituted ornon-substituted aralkyl group, substituted or non-substituted arylaminegroup, substituted or non-substituted alkylamine group, substituted ornon-substituted aralkylamine group, and substituted or non-substitutedheterocyclic group; and

each of Y, Y′ and Y″ represents a substituted or non-substitutedaromatic heterocycle that includes a 5-membered aromatic heterocyclecontaining A and X as ring members or a 6-membered aromatic heterocyclecontaining A and X as ring members, wherein Y, Y′ and Y″ are identicalor different.

The number of substituents present in Y, Y′ and Y″ is at least one andthe substituents are identical or different, each substituent beingselected from the group consisting of a halogen atom, nitrile group(CN), nitro group (NO₂), formyl group, acetyl group, benzoyl group,amide group, styryl group, acetyelene group, quinoline group,quinazoline group, phenanthroline group, cuproine group, anthraquinonegroup, benzoquinone group, quinone group, acridine group, substituted ornon-substituted alkyl group, substituted or non-substituted aryl group,substituted or non-substituted aralkyl group, substituted ornon-substituted arylamine group, substituted or non-substitutedalkylamine group, substituted or non-substituted aralkylamine group, andsubstituted or non-substituted heterocyclic group, wherein in some casestwo substituents adjacent to each other may form a fused ring together.

According to another aspect of the present invention, there is providedan organic light emitting device including a first electrode, an organicfilm having one or more layers and a second electrode, laminatedsuccessively, wherein at least one layer of the organic film includes atleast one compound represented by formula 1.

Hereinafter, the present invention will be explained in detail.

The present invention provides a compound represented by formula 1.

The compound represented by formula 1 is an organic substance includinga cyclic trimer core structure. The compound is capable of carrying outat least one function selected from the group consisting of holeinjection, hole transport, hole block, light emitting, electrontransport, electron injection, and buffering between an anode and a holeinjection layer, depending on the type of each unit forming the trimeror substituents in each unit. Particularly, the function of bufferingbetween an anode and a hole injection layer is required when interfacialcontact between them is poor, or when direct hole injection into a holeinjection layer is not made properly. Many compounds are known to carryout at least one function selected from the group consisting of holeinjection, hole transport, hole block, light emitting, electrontransport, electron injection, and buffering between an anode and a holeinjection layer. Most of them generally include a substituted ornon-substituted aromatic or heteroaromatic group.

Meanwhile, all kinds of compounds capable of carrying out at least onefunction selected from the group consisting of hole injection, holetransport, hole block, light emitting, electron transport, electroninjection, and buffering between an anode and a hole injection layer canbe prepared by varying the type of each trimer-forming unit orsubstituents present in each unit from the organic substance representedby the above formula 1 including a cyclic trimer core structure.Heretofore, it has not been known that all kinds of compounds capable ofcarrying out at least one function needed for a desired organic lightemitting device can be prepared by varying the type of each unit orsubstituents from one basic structure.

Organic substances that function as hole injection materials arecompounds facilitating hole injection from an anode. Preferably, suchcompounds have ionization potential suitable for hole injection from ananode, high interfacial adhesion to an anode, non-absorbability in thevisible light range, etc. Particular examples of units or substituentscapable of performing a function of a hole injection include organicsubstances of metal porphyrin, oligothiophen, arylamine series, organicsubstances of hexanitrile hexaazatriphenylene, quinacridone series,organic substances of perylene series, conductive polymers based onanthraquinone, polyaniline, and polythiophene or polymers such asdopants, but are not limited thereto.

Organic substances that function as hole transport materials preferablyhave high hole mobility and high LUMO energy level for electronblocking. Particular examples of units or substituents capable ofperforming a function of a hole transport may include organic substancesof arylamine series, conductive polymers and block copolymers havingboth conjugated portions and non-conjugated portions, but are notlimited thereto. Particular examples thereof include triarylaminederivatives, amines having a bulky aromatic group, starburst aromaticamines, spirofluorene-containing amines, crosslinked amines andanthracene-based compounds.

Organic substances that function as electron transport materials arethose having an electron withdrawing group. Units or substituentscapable of performing a function of an electron transport may includecompounds containing a functional group capable of withdrawing electronsby resonance (for example cyano, oxadiazole or triazole group).Particular exmples thereof include 8-hydroxyquinolone-Al complex;complexes including Alq3; organic radical compounds; and hydroxy-flavone-metal complexes, but are not limited thereto.

Organic substances that function as light emitting materials are thosehaving moieties capable of emitting light by accepting and recombiningholes and electrons and may include fluorescent materials andphosphorescent materials. Particular examples of units or substituentscapable of performing a function of a light emitting include8-hydroxyquinoline aluminum complex (Alq3); compounds of carbazoleseries; dimerized styryl compounds; BAlq3;10-hydroxybenzoquinoline-metal compounds; compounds of benzoxazole,benzthiazole and benzimidazole series; polymers based onpoly(p-phenylenevinylene) series; polymers based onpoly-phenylenevinylene (PPV); spiro compounds; and compounds ofpolyfluorene, rubrene and anthracene series, but are not limitedthereto.

Meanwhile, an organic substance designed by using the cyclic trimer corestructure represented by formula 1 has a molecular weight higher thanthat of each monomer forming the trimer. Accordingly, it has highthermal stability, thereby improving durability of an OLED including anorganic film formed by using the same. Additionally, when a monomericorganic substance used in a light emitting layer is trimerized, theresultant molecular weight increases accordingly, and thus it ispossible to obtain an organic substance having a long wavelength shiftedfrom a short wavelength (for example, from blue to red). Further, thecompound represented by formula 1 having a trimerized structure providesa suitable band gap between the HOMO and the LUMO and energy valuecompared to each monomer forming the trimer, thereby reducing drivevoltage.

Additionally, in the cyclic trimer core structure represented by formula1, the saturated 6-membered ring having three heteroatoms (A) forms anon-planar (for example, chair-like) structure like the structure ofcyclohexane, contrary to a flat aromatic ring. Therefore, three units,i.e.,

that are bonded symmetrically to the 6-membered ring form a non-planarpropeller-like structure in which they are distorted symmetrically toone another, so that steric hindrance among the three units can bereduced. Further, if each of the units (generally, substituted ornon-substituted aromatic compounds) forming the trimer is present as amonomer, the aromatic compounds are laminated together in the form of aflat plane and thus permit intermolecular interaction. However, ifmonomers are trimerized into the core structure represented by formula1, their amorphous characteristics can be exerted more. Therefore, it ispossible to prevent the breakdown of a device caused by crystallizationresulting from the Joule heat generated during the operation of an OLED.Further, the cyclic trimer core structure represented by formula 1 hasthree units bonded symmetrically to the non-planar 6-membered ring andthus it is possible to design organic substances having structures thatare not excessively planar but ordered. The above-describedcharacteristics are useful for an organic substance used in a holetransport layer or electron transport layer.

The cyclic trimer represented by formula 1 does not permit extension ofconjugation among units because of the saturated 6-membered ring, andthus each unit can function independently from each other. Therefore, itis possible to contemplate each unit individually and to facilitatemolecular designs. For example, each unit can be derived from a monomerhaving a function different from each other. Additionally, when amonomeric organic substance used in a light emitting layer is trimerizedinto a cyclic form at meta-positions as depicted in formula 1, itsmolecular weight increases followed by a wavelength shift to a longwavelength. In this case, the saturated 6-membered ring prevents furtherextension of conjugation, and thus can reduce a shift range compared toa linear polymer obtained from the monomer.

In formula 1, A is preferably a nitrogen atom (N).

In formula 1, X is preferably a nitrogen atom (N).

In formula 1, when substituents attached to Y, Y′ and Y″ include analkyl group, the length of the alkyl group does not significantly affectthe compound of formula 1 in carrying out at least one function selectedfrom the group consisting of hole injection, hole transport, hole block,light emitting, electron transport, electron injection, and bufferingbetween an anode and a hole injection layer. Light absorption oremission in an electronic device can be affected by the conjugationlength of a functional compound. Because the length of an alkyl groupincluded in the compound does not affect the conjugation length of thecompound, it has no direct effect on the wavelength of the compound oron characteristics of a device. However, the length of an alkyl groupmay affect the selection of a method of applying the compound to an OLED(for example, a vacuum deposition method or a solution coating method).Therefore, there is no particular limitation in length of alkyl groupsthat may be included in the structure represented by formula 1.

One example of the compound represented by formula 1 is a compoundrepresented by the following formula 2:

wherein

A and X are the same as defined above with regard to formula 1; and

R1 to R6 are identical or different and each is selected from the groupconsisting of a hydrogen atom (H), halogen atom, nitrile group (CN),nitro group (NO₂), formyl group, acetyl group, benzoyl group, amidegroup, styryl group, acetylene group, quinoline group, quinazolinegroup, phenanthroline group, cuproine group, anthraquinone group,benzoquinone group, quinone group, acridine group, substituted ornon-substituted alkyl group, substituted or non-substituted aryl group,substituted or non-substituted aralkyl group, substituted ornon-substituted arylamine group, substituted or non-substitutedalkylamine group, substituted or non-substituted aralkylamine group, andsubstituted or non-substituted heterocyclic group, wherein in some casesR1 and R2, R3 and R4, and R5 and R6 may form a fused ring with eachother.

Another example of the compound represented by formula 1 is a compoundrepresented by the following formula 3:

wherein

A and X are the same as defined above with regard to formula 1; and

R1 to R18 are identical or different and have the same meanings as R1 toR6 in the above formula 2, wherein in some cases each of R1 to R18 mayform a fused ring together with a substituent adjacent thereto.

Non-limitative examples of the substituents in formulae 1-3 (for exampleR₀ to R18) will be described hereinafter.

Halogen atoms include a fluorine (F), chlorine (Cl), bromine (Br) andiodine (I) atoms.

Alkyl groups preferably have 1 to 20 of carbon atoms (C1-C20) andinclude linear alkyl groups such as methyl, ethyl, propyl, hexyl, etc.,and branched alkyl groups such as isopropyl, tert-butyl, etc.

Aryl groups include monocyclic aromatic cycles such as phenyl, etc., andmulticyclic aromatic cycles such as naphthyl, anthryl, pyrene, perylene,etc.

Aralkyl groups include C1-C20 alkyl groups substituted with aromatichydrocarbons such as phenyl, biphenyl, naphthyl, terphenyl, anthryl,pyrene, perylene, etc.

Arylamine groups include amine groups substituted with aromatichydrocarbons such as phenyl, biphenyl, naphthyl, terphenyl, anthryl,pyrene, perylene, etc.

Alkylamine groups include amine groups substituted with C1-C20 aliphatichydrocarbons.

Aralkylamine groups include amine groups substituted with aromatichydrocarbons such as phenyl, biphenyl, naphthyl, terphenyl, anthryl,pyrene, perylene, etc., and C1-C20 aliphatic hydrocarbons.

Heterocyclic groups include pyrrolyl, thienyl, indole, oxazole,imidazole, thiazole, pyridyl, pyrimidine, piperazine, thiophene, furan,pyridazinyl, etc.

In formulae 2 and 3, fused rings formed by each of R1 to R18 with asubstituent adjacent thereto include pyrrole, furan, thiophene, indole,oxazole, imidazole, thiazole, pyridine, pyrizine, benzene, naphthalene,pyrazine, quinoline, quinazoline, phenanthroline, cuproine,anthraquinone, benzoquinone, quinone, acridine, etc.

Further, each of substituted alkyl, aryl, aralkyl, arylamine,alkylamine, aralkylamine and heterocyclic groups in R₀ to R18 may haveone or more substituents selected from the group consisting of a halogenatom including fluorine, chlorine, bromine and iodine, nitrile, nitro,formyl, acetyl, arylamine, alkylamine, aralkylamine, benzoyl, amide,styryl, acetylene, phenyl, naphathyl, anthryl, pyrene, perylene,pyridyl, pyridazyl, pyrrolyl, imidazolyl, quinolyl, anthrone, acridone,acridine, etc.

Particular examples of the compound represented by formula 1 include thecompounds represented by formulae 1-1 to 1-46, but are not limitedthereto:

wherein n is an integer of between 1 and 6.

wherein n is an integer of at least 1.

wherein n is an integer of at least 1.

Additionally, the compound represented by formula 1 (for example,compound represented by formulae 1-1 or 1-35) can be used as aphosphorescence host, which may be used together with a phosphorescencedopant, in an organic phosphorescence light emitting device.

Meanwhile, as can be seen from the following Example 1, the compoundrepresented by formula 1-1 is a substance that functions as an electroninjection/transport material. Further, it can be seen indirectly thatthe compound represented by formula 1-1 is an n-type substance.Therefore, it can be seen that compounds having the compound representedby formula 1-1 as a core also function as electron injection/transportmaterials. Each monomer (benzimidazole) forming the trimeric compoundrepresented by formula 1-1 cannot be applied to an organic film in anOLED by itself, because the band gap between the HOMO and the LUMO islarge, it has no electron mobility and it has such a small molecularweight as to be sublimated easily. However, when a cyclic trimerrepresented by formula 1 is formed from such a monomer, it is possibleto increase the molecular weight, to reduce the band gap between theHOMO and the LUMO and to impart electron mobility. Accordingly, even ifa compound cannot function as a material for hole injection, holetransport, hole block, light emitting, electron transport, electroninjection, and buffering between an anode and a hole injection layer, orthe like, it is possible to cause the compound to have theabove-described functions by forming a cyclic trimer represented byformula 1 from the compound as a monomer.

Meanwhile, the organic substance represented by formula 1-12 has a corerepresented by formula 1-1 having n-type characteristics and arylaminesubstituents imparting p-type characteristics, and thus can function asa hole transport material, as can be seen from the following Example 2.Therefore, compounds having a core represented by formula 1 can providematerials having p-type characteristics, n-type characteristics oramphoteric characteristics depending on the characteristics ofsubstituents. Further, such characteristics depending on substituentsdetermine an organic layer in an OLED that a compound represented byformula 1 can be used.

The compound represented by formula 1 can be prepared by using thefollowing starting materials:

Particularly, non-limitative examples of the starting materials includethe following compounds:

wherein A, X and R1 to R6 as substituents for Y, Y′ and Y″ are the sameas defined above with regard to formula 1, 2 or 3; and Z is a halogenatom. Particularly, Z may be selected from the group consisting of F,Cl, Br and I.

According to the present invention, compounds represented by formula 1may be prepared by trimerizing the starting materials and optionallyintroducing substituents to the resultant trimeric compounds ifnecessary. Trimerization or substituent introduction may be performed byusing any conventional methods known to one skilled in the art. Further,solvents may be used in synthetic routes, if desired. For example, adesired trimer compound can be prepared by heating at least one compoundselected from the above starting materials to 200-300° C. Preparation oftrimer compounds will be explained in detail through the followingPreparation Examples. However, it is to be understood that methodsdescribed in the following Preparation Examples can be modified by oneskilled in the art in order to prepare compounds according to thepresent invention.

The present invention also provides an organic light emitting device(OLED) including a first electrode, an organic film having one or morelayers and a second electrode, laminated successively, wherein at leastone layer of the organic film contains at least one compound representedby formula 1.

In the OLED according to the present invention, the organic filmcontaining the compound represented by formula 1 may be formed by usinga vacuum deposition method or a solution coating method. Particularexamples of the solution coating method include spin coating, dipcoating, doctor blade coating, ink-jet printing or heat transfer method,but are not limited thereto.

The organic film containing the compound represented by formula 1 mayhave a thickness of 10 μm or less, preferably 0.5 μm or less, and morepreferably 0.001-0.5 μm.

The compound represented by formula 1 may be used together with otherknown materials that function as materials for hole injection, holetransport, light emitting, electron transport or electron injection (ifnecessary).

The OLED according to the present invention may have a structure havingan organic film including a hole injection layer, a hole transportlayer, a light emitting layer, an electron transport layer, an electroninjection layer and a buffering layer disposed between an anode and thehole injection layer. However, the structure of OLED is not limitedthereto and the number of layers included in the organic film may bereduced.

According to the invention, organic light emitting devices (OLED) mayhave structures as shown in FIGS. 1 to 5, but the embodiments shown inthe figures are not limitative.

FIG. 1 shows an OLED having a structure in which an anode 102, a lightemitting layer 105 and a cathode 107 are laminated successively on asubstrate 101.

FIG. 2 shows an OLED having a structure in which an anode 102, a holetransport/light emitting layer 105, a light emitting/electron transportlayer 106 and a cathode 107 are laminated successively on a substrate101.

FIG. 3 shows an OLED having a structure in which an anode 102, a holetransport layer 104, a light emitting layer 105, an electron transportlayer 106 and a cathode 107 are laminated successively on a substrate101.

FIG. 4 shows an OLED having a structure in which an anode 102, a holeinjection layer 103, a hole transport layer 104, a light emitting layer105, an electron transport layer 106 and a cathode 107 are laminatedsuccessively on a substrate 101.

FIG. 5 shows an OLED having a structure in which an anode 102, a holeinjection layer 103, a hole transport layer 104, a light emitting layer105, a hole block layer 108, an electron transport layer 106 and acathode 107 are laminated successively on a substrate 101.

In the structures illustrated in FIGS. 1 to 5, the compound representedby formula 1 may form the hole injection layer 103, hole transport layer104, light emitting layer 105, hole block layer 108, electron transportlayer 106, electron transport/light emitting layer 105 and/or lightemitting/electron transport layer 106.

As shown in FIGS. 1 to 5, OLEDs according to the present invention havea structure in which an anode, a multi-layered organic film and acathode are successively laminated. Additionally, an insulation layer oradhesive layer may be inserted into the interface between each electrodeand the organic film. Further, the hole transport layer present in theorganic film may be formed of two layers each having a different valueof ionization potential.

OLEDs according to the present invention can be prepared by forming anorganic film and electrodes by using materials and methods known to oneskilled in the art, with the proviso that at least one layer of theorganic film contains the compound according to the present invention.

For example, substrates 101 that may be used include a silicon wafer,quartz or glass panel, metal panel, plastic film or sheet, etc.

Materials for anode 102 may include metals such as vanadium, chrome,copper, zinc and gold or alloys thereof; metal oxides such as zincoxide, indium oxide, indium tin oxide (ITO) and indium zinc oxide;metal/oxide composites such as ZnO:Al or SnO₂:Sb; and conductivepolymers such as poly(3-methylthiophene),poly[3,4-(ethylene-1,2-dioxy)thiophene] (PEDT), polypyrrole andpolyaniline, but are not limited thereto.

Materials for cathode 107 may include metals such as magnesium, calcium,sodium, potassium, titanium, indium, yttrium, lithium, gadolinium,aluminum, silver, tin and lead or alloys thereof; and multi-layeredmaterials such as LiF/Al or LiO₂/Al, but are not limited thereto.

Advanced Effect

According to the present invention, it is possible to provide an organicsubstance capable of carrying out at least one function selected fromthe group consisting of hole injection, hole transport, hole block,light emitting, electron transport, electron injection, and bufferingbetween an anode and a hole injection layer through molecular designsusing a cyclic trimer core structure represented by formula 1. Further,it is possible to improve durability and/or efficiency of an organiclight emitting device by using the organic substance in an organic filmof the device.

Mode for Carrying Out the Invention

Hereinafter, the present invention will be explained in more detailthrough Preparation Examples 1-6, Examples 1 and 2, and ComparativeExamples 1 and 2. It is to be understood that the following examples areillustrative only and the present invention is not limited thereto.

PREPARATION EXAMPLE 1 Synthesis of Compounds of Formula 1-1(Trimerization of 2-chlorobenzimidazole)

5 g (0.0327 mole) of 2-chlorobenzimidazole as a starting material wasintroduced into a 50 mL long-necked flask and the flask was immersed inan oil bath preheated to 195° C. Hereupon, the starting material wasdissolved and transformed back into a solid state immediately, whilegenerating hydrogen chloride gas. When the gas stopped bubbling, thereaction mixture was cooled to room temperature and the resultant solidcompound was recrystallized with nitrobenzene. Then, the product wasfiltered, washed with ethanol and ether in turn then dried under vacuumto obtain the compound represented by formula 1-1 as a white solid (2.5g, yield 50%).

The analysis results for the compound are as follows: m.p. 391-393° C.;¹H NMR (500 MHz, DMSO-d6) 8.51 (d, 3H), 7.96 (d, 3H), 7.59 (m, 6H); MS[M+1] 348.

PREPARATION EXAMPLE 2 Synthesis of Compound of Formula 1-5(Trimerizationof 1-iodo-2-chloro-4,5-dicyanoimidazole)

10 g (0.036 mole) of 1-iodo-2-chloro-4,5-dicyanoimidazole as a startingmaterial was introduced into a 50 mL long-necked flask equipped with asublimation device. Then, the flask was purged with nitrogencontinuously two times under vacuum and immersed in an oil bathpreheated to 220-240° C. After maintaining the above temperature for 5hours, I₂ and ICl as halogen decomposition products were formed on acold finger. After cooling back to room temperature, the flask waspurged with nitrogen under vacuum. The resultant brown solid waspulverized and 10% Na₂S₂O₃ (40 mL) was added thereto. Then, the mixturewas stirred for 30 minutes at room temperature and then filtered (threetimes). The filtered solid was washed with water repeatedly and thendried under vacuum to obtain the compound represented by formula 1-5 asa yellowish brown solid (2.92 g, yield 70%).

The analysis results for the compound were as follows: purity 99.6%;m.p. >400° C.; ¹³C NMR (400 MHz, DMSO-d₆, ppm) 135.0, 123.2, 110.3,106.5, 106.2

PREPARATION EXAMPLE 3 Synthesis of Compound of Formula 1-6(Trimerization of 4,5-diphenylimidazole)

2.0 g (0.0091 mole) of 4,5-diphenylimidazole as a starting material,0.01 g of dichloropalladium, 0.3 g of sulfur, 0.1 mL of phenylthioetherand 10 mL of phenylether were introduced into a 50 mL round-bottom flaskequipped with a condenser. The reaction mixture was reacted under refluxand then cooled. Then, 50 mL of ether was added thereto to formprecipitate. The precipitate was removed by using a depressurized filterand then the filtrate was distilled under reduced pressure to remove allsolvents therefrom. Then, the resultant product was dissolved into 10 mLof dioxane at 90-100° C. and 15 mL of acetic acid was added thereto toperform recrystallization. The resultant product was filtered by using adepressurized filter to obtain a dark gray solid. The dark gray solidwas purified by sublimation to obtain the compound represented byformula 1-6 as a greenish white solid (0.6 g, yield 30%).

The analysis results for the compound were as follows: purity 99.6%;m.p. 361-363° C.; ¹H NMR (400 MHz, DMSO-d₆) 7.60-7.64 (m, 5H), 7.23-7.16(m, 5H); MS [M+1]⁺ 655, [M]⁻ 654

PREPARATION EXAMPLE 4

(1) Synthesis of Compound of Formula 4a

To a mixture containing 2-chlorobenzimidazole (0.763 g, mmol) as astarting material dissolved in 25 mL of methanol, bromine/methanolsolution (0.26 mL/5 mL) was gradually added dropwise. Then, the reactionmixture was stirred for 5 hours at room temperature. After checking areaction degree by HPLC, 25 mL of water was added and the mixture wasstirred for 18 hours at room temperature. The resultant precipitate wasfiltered and washed with cold water repeatedly until it became neutral.Then, the resultant product was recrystallized with methanol/water (1:1)solution to obtain the compound of formula 4a as a white solid (0.6 g,yield 52.0%).

The analysis results for the compound were as follows: m.p. 228-230° C.;¹H NMR (400 MHz, DMSO-d₆) 7.73 (s, 1H), 7.49-7.47 (d, 1H), 7.39-7.36 (d,1H); MS [M+1]⁺ 231

(2) Synthesis of Compound of Formula 4b (Trimerization of5-bromo-2-chlorobenzimidazole)

1.1 g (4.7 mmole) of 5-bromo-2-chlorobenzimidazole as a startingmaterial was introduced into a 50 mL long-necked flask and was immersedin an oil bath preheated to 230° C. Hereupon, the starting material wasdissolved and transformed back into a solid state immediately, whilegenerating hydrogen chloride gas. When the gas stopped bubbling, thereaction mixture was cooled to room temperature and the resultant solidcompound was recrystallized with nitrobenzene. Then, the product wasfiltered, washed with ethanol and ether in turn and then dried undervacuum to obtain the compound represented by formula 4b as a pale yellowsolid (0.43 g, yield 47%).

The analysis results for the compound are as follows: m.p. 354° C.; MS[M+1] 583 (isomer)

(3) Synthesis of Compound of Formula 1-12

To a 50 mL round-bottom flask equipped with a condenser, sequentiallyadded were a mixed solution containing 10 mL of mesitylene and thecompound of formula 4b (0.4 g, 0.68 mmol), 50 mg of Pd₂(dba)₃ (0.005mmol), 17 mg of P(t-Bu)₃ (0.081 mmol), and 0.28 g of Na(t-OBu) (3 mmol).The reaction mixture was reacted for 5 hours at 120° C. After thereaction mixture was cooled to room temperature, 20 mL of toluene and 30mL of water were added thereto to perform phase separation. The organiclayer obtained from the preceding step was dried over MgSO₄ and thedried product was distilled under reduced pressure to remove allsolvents therefrom. The product was separated by column chromatographyand then washed with ethanol to obtain the compound of formula 1-12 as awhite solid (200 mg, yield 30%).

The analysis results for the compound were as follows: m.p. ≧350° C.; ¹HNMR (500 MHz, DMSO-d6) 8.27-8.15 (m, 1H), 8.09-7.74 (m, 3H), 7.63-7.16(m, 8H), 6.97-6.86 (m, 3H); MS [M+1] 1000

PREPARATION EXAMPLE 5

(1) Synthesis of Compound of Formula 5b (2-chloroperimidine)

Purified 1,8-diaminonaphthalene (1.7 g, 10.7 mmol) was introduced into30 mL of diluted hydrochloric acid solution (0.5N) and heated to becompletely dissolved. After 10 mL of aqueous sodium cyanide solution(0.7 g, 10.7 mmol) was gradually added thereto, red precipitate wasformed. The red precipitate was heated for 1 hour and cooled. Then, theresultant precipitate was filtered, washed with ether and then driedunder vacuum to obtain 2-perimidinone (5a) as a pale reddish white solid(1.12 g, 6.1 mmol, yield 57%). The resultant solid was added to 10 mL ofphosphorous oxychloride (POCl₃) and refluxed for 3 hours by heating.Then, excessive amount of phosphorous oxychloride was removed by vacuumdistillation. The residue was dispersed in water and neutralized with 2Naqueous ammonia to form yellow precipitate. The precipitate was filteredand the filtrate was precipitated again by using THF and hexane assolvents. Then, the solution was filtered again and the filtered productwas dried under vacuum to obtain 2-chloroperimidine as a light yellowsolid (0.6 g, 2.9 mmol, yield 50%).

The analysis results for the above compounds were as follows:

2-perimidinone (5a): ¹H NMR (400 MHz, DMSO-d₆), 10.06 (s, 2H), 7.21 (t,J=7.6 Hz, 2H), 7.10 (d, J=8.4 Hz, 2H), 6.51 (d, J=7.6 Hz, 2H)

2-chloroperimidine (5b): ¹H NMR (400 MHz, DMSO-d₆), 11.35 (s, 1H),7.20-7.08 (m, 4H), 6.60 (d, J=6.4 Hz, 1H), 6.38 (d, J=6.8 Hz, 1H)

(2) Synthesis of Compound of Formula 1-46

2-chloroperimidine (0.73 g, 3.6 mmol) was introduced into a flaskequipped with a mechanical stirrer under nitrogen atmosphere and heatedto 210° C. to dissolve it. After stirring for 10 minutes, the mixtureturned dark red. About 20 mL of nitrobenzene was added thereto, and themixture was stirred for about 1 hour, cooled and filtered to separateprecipitate. The filtered product was washed sufficiently withnitrobenzene, saturated sodium carbonate solution, water, ethanol andTHF, in turn, and then was dried under vacuum to obtain 0.57 g of thecompound represented by formula 1-46 as a red solid (yield 32%).

The analysis results for the compound were as follows: ¹H NMR (400 MHz,DMSO-d₆), 7.52-7.28 (m, 12H), 6.94-6.80 (m, 6H); MS (M+HCl+H) 535

EXAMPLE 1

(Manufacture of Organic Light Emitting Device)

A glass substrate on which a thin film of ITO (indium tin oxide) wascoated to a thickness of 1500 Å was immersed in distilled watercontaining a detergent to wash the substrate with ultrasonic waves for30 minutes. Next, washing with ultrasonic waves was repeated for 10minutes and two times by using distilled water. The detergent was aproduct commercially available from Fisher Co. The distilled water hasbeen filtered previously by using a filter commercially available fromMillipore Co. After the completion of washing with distilled water,washing with ultrasonic waves was carried out by using solvents such asisopropyl alcohol, acetone and methanol, in turn. The resultant productwas dried and transferred to a plasma cleaner. Then, the substrate wascleaned for 5 minutes by using nitrogen plasma and transferred to avacuum deposition device.

On the ITO transparent electrode prepared as described above,hexanitrile hexaazatriphenylene represented by the following formula 4was coated to a thickness of 500 Å by thermal vacuum deposition, therebyforming a hole injection layer. Next, NPB as a hole transport materialwas coated thereon to a thickness of 400 Å by vacuum deposition.Additionally, a light emitting compound (Alq3) represented by thefollowing formula 5 was coated thereon to a thickness of 300 Å by vacuumdeposition to form a light emitting layer. On the light emitting layer,the compound represented by formula 1-1 was coated to a thickness of 200Å by vacuum deposition to form an electron injection/transport layer.Next, on the electron injection/transport layer, lithium fluoride (LiF)and aluminum were sequentially vacuum-deposited to a thickness of 10 Åand 2500 Å, respectively, to form a cathode. In the above process,deposition rate of each organic substance was maintained at 1 Å/sec anddeposition rates of lithium fluoride and aluminum were maintained at 0.2Å/sec and 3-7 Å/sec, respectively.

The resultant organic light emitting device showed a drive voltage of3.57V at a forward current density of 10 mA/cm². Further, specific greenspectrum of Alq3 was observed with x=3.94 and y=0.56 based on the 1931CIE color coordinate. Such light emitting operation of the device at theabove drive voltage indicates that the compound of formula 1-1 containedin the layer disposed between the light emitting layer and the cathodecan function as an electron injection/transport material.

Comparative Example 1

Example 1 was repeated to manufacture an organic light emitting device,except that Alq3, a conventional compound useful for electron injectionand transport was coated on the light emitting layer to a thickness of200 Å by vacuum deposition, instead of the compound of formula 1-1, toform an electron injection/transport layer.

The resultant organic light emitting device showed a drive voltage of4.12V at a forward current density of 10 mA/cm². Further, specific greenspectrum of Alq3 was observed with x=0.34 and y=0.56 based on the 1931CIE color coordinate.

The following Table 1 shows the results of variations in drive voltagedepending on currents for the organic light emitting devices obtainedfrom Example 1 and Comparative Example 1.

TABLE 1 Example 1 Comp. Ex. 1 Current density (mA/cm²) Voltage (V)Voltage (V) 10 3.57 4.12 50 4.82 5.67 100 5.62 6.59

As can be seen from Table 1, when an electron injection/transport layerfor an organic light emitting device is formed by using the compound offormula 1-1, the drive voltage can be reduced under the same currentdensity, compared to an organic light emitting device using Alq3 that isa conventional material functioning as an electron injection/transportlayer.

EXAMPLE 2

On the ITO transparent electrode prepared as described in Example 1,hexanitrile hexaazatriphenylene represented by formula 4 was coated to athickness of 500 Å by thermal vacuum deposition, thereby forming a holeinjection layer. Next, the compound of formula 1-12 obtained fromPreparation Example 4, as a hole transport material, was coated thereonto a thickness of 200 Å by vacuum deposition. Additionally, a lightemitting compound (Alq3) represented by formula 5 was coated thereon toa thickness of 300 Å by vacuum deposition to form a light emittinglayer. On the light emitting layer, the compound represented by thefollowing formula 6 was coated to a thickness of 200 Å by vacuumdeposition to form an electron injection/transport layer. Next, on theelectron injection/transport layer, lithium fluoride (LiF) and aluminumwere sequentially vacuum-deposited to a thickness of 10 Å and 2500 Å,respectively, to form a cathode. In the above process, deposition rateof each organic substance was maintained at 1 Å/sec and deposition ratesof lithium fluoride and aluminum were maintained at 0.2 Å/sec and 3-7Å/sec, respectively.

The resultant organic light emitting device showed a light emittingefficiency of 460 cd/cm² at a forward current density of 100 mA/cm².Further, specific green spectrum of Alq3 was observed with x=0.32 andy=0.56 based on the 1931 CIE color coordinate. Such light emittingoperation of the device at the above drive voltage indicates that thecompound of formula 1-12 contained in the layer disposed between thehole injection layer and the light emitting layer can function as a holetransport material.

Comparative Example 2

Example 2 was repeated to manufacture an organic light emitting device,except that NPB, a conventional compound useful for hole transport wascoated on the hole injection layer to a thickness of 200 Å by vacuumdeposition, instead of the compound of formula 1-12, to form a holetransport layer.

The resultant organic light emitting device showed a light emittingefficiency of 340 cd/cm² at a forward current density of 100 mA/cm².Further, specific green spectrum of Alq3 was observed with x=0.32 andy=0.56 based on the 1931 CIE color coordinate.

As can be seen from Example 2 and Comparative Example 2, when an organiclight emitting device includes the compound represented by formula 1-12in a hole transport layer, the light emitting efficiency can be improvedunder the same current density, compared to an organic light emittingdevice including NPB in a hole transport layer.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiment and the drawings. On the contrary, it is intendedto cover various modifications and variations within the spirit andscope of the appended claims.

1. An organic light emitting device including a first electrode, anorganic film having one or more layers and a second electrode, laminatedsuccessively, wherein at least one layer of the organic film includes atleast one compound represented by Formula 1:

wherein A is B or N; X is N or CR₀, wherein R₀ is selected from thegroup consisting of a hydrogen atom (H), halogen atom, nitrile group(CN), nitro group (NO₂), formyl group, acetyl group, benzoyl group,amide group, styryl group, acetylene group, quinoline group, quinazolinegroup, phenanthroline group, cuproine group, anthraquinone group,benzoquinone group, quinone group, acridine group, substituted ornon-substituted alkyl group, substituted or non-substituted aryl group,substituted or non-substituted aralkyl group, substituted ornon-substituted arylamine group, substituted or non-substitutedalkylamine group, substituted or non-substituted aralkylamine group, andsubstituted or non-substituted heterocyclic group; and wherein each ofY, Y′ and Y″ represents a substituted or non-substituted aromaticheterocycle that includes a 5-membered aromatic heterocycle containing Aand X as ring members or a 6-membered aromatic heterocycle containing Aand X as ring members, wherein Y, Y′ and Y″ are identical or different.2. The organic light emitting device according to claim 1, wherein eachof Y, Y′ and Y″ is substituted with one or more identical or differentsubstituents selected from the group consisting of a halogen atom,nitrile group (CN), nitro group (NO₂), formyl group, acetyl group,benzoyl group, amide group, styryl group, acetylene group, quinolinegroup, quinazoline group, phenanthroline group, cuproine group,anthraquinone group, benzoquinone group, quinone group, acridine group,substituted or non-substituted alkyl group, substituted ornon-substituted aryl group, substituted or non-substituted aralkylgroup, substituted or non-substituted arylamine group, substituted ornon-substituted alkylamine group, substituted or non-substitutedaralkylamine group, and substituted or non-substituted heterocyclicgroup, wherein two substituents adjacent to each other are not fused orform a fused ring together.
 3. The organic light emitting deviceaccording to claim 1, wherein the compound is represented by formula 2:

wherein A and X are the same as defined in claim 1; and R1 to R6 areidentical or different and each is selected from the group consisting ofa hydrogen atom (H), halogen atom, nitrile group (CN), nitro group(NO₂), formyl group, acetyl group, benzoyl group, amide group, styrylgroup, acetylene group, quinoline group, quinazoline group,phenanthroline group, cuproine group, anthraquinone group, benzoquinonegroup, quinone group, acridine group, substituted or non-substitutedalkyl group, substituted or non-substituted aryl group, substituted ornon-substituted aralkyl group, substituted or non-substituted arylaminegroup, substituted or non-substituted alkylamine group, substituted ornon-substituted aralkylamine group, and substituted or non-substitutedheterocyclic group, wherein R1 and R2, R3 and R4, and R5 and R6optionally form a fused ring with each other.
 4. The organic lightemitting device according to claim 1, wherein the compound isrepresented by formula 3:

wherein A and X are the same as defined in claim 1; and R1 to R18 areidentical or different and each is selected from the group consisting ofa hydrogen atom (H), halogen atom, nitrile group (CN), nitro group(NO₂), formyl group, acetyl group, benzoyl group, amide group, styrylgroup, acetylene group, quinoline group, quinazoline group,phenanthroline group, cuproine group, anthraquinone group, benzoquinonegroup, quinone group, acridine group, substituted or non-substitutedalkyl group, substituted or non-substituted aryl group, substituted ornon-substituted aralkyl group, substituted or non-substituted arylaminegroup, substituted or non-substituted alkylamine group, substituted ornon-substituted aralkylamine group, and substituted or non-substitutedheterocyclic group, wherein each of R1 to R18 optionally form a fusedring together with a substituent adjacent thereto.
 5. The organic lightemitting device according to claim 1, wherein the compound is selectedfrom the group consisting of compounds represented by formulae 1-1 to1-18 and 1-20 to 1-46: